Calibration of a position measuring device of an optical device

Abstract

A method for calibrating a position measuring device of an optical device, including a measurement step in which a movable unit of the optical device is moved according to a predefinable scheme in at least one degree of freedom and a position of the movable unit is determined in the at least one degree of freedom. The position of the movable unit is determined in the at least one degree of freedom in a first measurement via a first measuring device of the position measuring device, and the position of the movable unit is determined in the at least one degree of freedom in a second measurement via a second measuring device of the position measuring device sing a reference element connected to the movable unit. In a calibration step, the first measuring device is calibrated using the results of the first measurement and the second measurement. An encoder system is used as the second measuring device. The reference element includes a reference grid of the encoder system.

1. A method of calibrating a position measuring device, the method comprising:
 moving a movable unit of an optical device according to a first predefinable scheme in at least one degree of freedom; 
 in a first measurement step, determining a first position of the movable unit in the at least one degree of freedom in first and second measurements, the first measurement being performed via a first measuring device of the position measuring device, and the second measurement being performed via a second measuring device of the position measuring device using a reference element connected to the movable unit; and 
 in a first calibration step, calibrating the first measuring device based on results of the first and second measurements, 
 wherein the second measuring device comprises an encoder system, and the reference element comprises a reference grid of the encoder system. 
 
     
     
       2. The method according to  claim 1 , wherein:
 the encoder system comprises a two-dimensional encoder system; 
 the grid comprises a two-dimensional grid; and/or 
 the encoder system has a resolution below one nanometer. 
 
     
     
       3. The method according to  claim 1 , wherein the reference element has a low thermal coefficient, and/or the reference element is thermally stabilised via a thermal stabilisation device. 
     
     
       4. The method according to  claim 1 , further comprising, in a second measurement step:
 moving the movable unit according to a second predefinable scheme in the at least one degree of freedom; and 
 determining a second position of the movable unit in the at least one degree of freedom in third and fourth measurements, the third measurement being performed via the first measuring device, and the fourth measurement being performed via the second measuring device using the reference element, 
 wherein the first calibration step comprises calibrating the first measuring device based on results of the first, second, third and fourth measurements. 
 
     
     
       5. The method according to  claim 4 , wherein the movable unit is moved in the second measurement step according to the same scheme as in the first measurement step. 
     
     
       6. The method according to  claim 4 , wherein:
 in the first measurement step, the reference element has a first position and a first orientation with respect to the movable unit; 
 before the second measurement step, the reference element is moved to a predefinable second position and/or a predefinable second orientation with respect to the movable unit; and 
 the first position is different from the second position, and/or the first orientation is different from the second orientation. 
 
     
     
       7. The method according to  claim 4 , wherein:
 in the second measurement, the position of the movable unit is determined in the at least one degree of freedom using a first measuring unit of the second measuring device; 
 in the fourth measurement, the position of the movable unit is determined in the at least one degree of freedom using a second measuring unit of the second measuring device; and 
 relative to the first measuring unit, the second measuring unit is displaced transversely with respect to the direction along the at least one degree of freedom. 
 
     
     
       8. The method according to  claim 4 , further comprising, in a third measurement step:
 moving the movable unit according to a third predefinable scheme in the at least one degree of freedom; and 
 determining a third position of the movable unit in the at least one degree of freedom via fifth and sixth measurements, the fifth measurement being performed via the first measuring device, the sixth measurement being performed via the second measuring device using the reference element, 
 wherein the first calibration step comprises calibrating the first measuring device based on results of the first, second, third, fourth, fifth and sixth measurements. 
 
     
     
       9. The method according to  claim 8 , wherein the movable unit is moved in the third measurement step according to the same scheme as in the first and second measurement steps. 
     
     
       10. The method according to  claim 8 , wherein:
 in the first measurement step, the reference element has a first position and first orientation with respect to the movable unit; 
 before the second measurement step, the reference element is moved to a predefinable second position with respect to the movable unit; and 
 before the third measurement step, the reference element is moved to a predefinable third orientation with respect to the movable unit, and 
 wherein:
 the first position and second positions are different from each other, and the first orientation and the third orientation are different from each other; or 
 before the second measurement step, the reference element is moved to a predefinable second predefinable second orientation with respect to the movable unit; and, before the third measurement step, the reference element is moved to a predefinable third position with respect to the movable unit; the first and third positions are different from each other; and the first and second orientations are different from each other. 
 
 
     
     
       11. The method according to  claim 8 , wherein:
 in the first calibration step, at least the results of the second and fourth measurements are evaluated to eliminate a systematic error of the encoder system, wherein a result of the evaluation is stored in a reference dataset; 
 after the first calibration step:
 moving the movable unit according to a fourth predefinable scheme in the at least one degree of freedom; and 
 determining a fourth position of the movable unit via seventh and eighth measurements, the seventh measurement being performed via the first measuring device, and the eighth measurement being performed via the second measuring device using the reference; and 
 
 in a second calibration step, calibrating the first measuring device using the reference dataset and results of the seventh and eighth measurements. 
 
     
     
       12. The method according to  claim 1 , wherein:
 the movable unit defines a first region, the position of the region being determined via the first measuring device in a normal operation of the optical device; 
 at least in the second measurement, the second measuring device captures a measuring region of the reference element; and 
 the measuring region is arranged at least close to the first region. 
 
     
     
       13. The method according to  claim 1 , wherein:
 the optical device defines a region in which the movable unit is moved in a normal operation of the optical device; and 
 in the first measurement step, the movable unit is moved in the at least one degree of freedom at least over a large part of the region. 
 
     
     
       14. The method according to  claim 1 , wherein, during the second measurement, at least one reference mark of the reference element is captured by the second measuring device. 
     
     
       15. The method according to  claim 1 , wherein the method is used to calibrate:
 a) a position measuring device of a mask table of a microlithography device; 
 b) a position measuring device of a substrate table of a microlithography device; 
 c) a position measuring device of a substrate table of a substrate inspection device; or 
 d) a position measuring device of a mask table of a mask inspection device. 
 
     
     
       16. An optical device, comprising:
 a movable unit configured to be moved by a drive unit; 
 a control device; and 
 a position measuring device, comprising:
 a first measuring device; and 
 a second measuring device, 
 
 wherein:
 the position measuring device is configured to determine, in a measurement step, a position of the movable unit moved by the drive unit according to a predefinable scheme in at least one degree of freedom; 
 the first measuring device is configured to determine, in a first measurement, a first variable which is representative of the position of the movable unit in the at least one degree of freedom and to provide the first variable to the control device; 
 the second measuring device comprises a reference element which is connected to the movable unit and is configured to determine, in a second measurement, using the reference element, a second variable which is representative of the position of the movable unit in the at least one degree of freedom and to provide the second variable to the control device; 
 the control device is configured to calibrate, in a calibration step, the first measuring device using the results of the first measurement and the second measurement; 
 the second measuring device comprises an encoder system; 
 the reference element comprises a reference grid of the encoder system; and 
 the optical device is configured to be used in microlithography. 
 
 
     
     
       17. The device according to  claim 16 , wherein the encoder system comprises a two-dimensional encoder system with a two-dimensional reference grid, and/or the encoder system has a resolution below one nanometer. 
     
     
       18. The optical device according to  claim 16 , wherein the reference element has a low thermal coefficient of expansion, and/or a thermal stabilisation device is provided, which is configured to thermally stabilise the reference element. 
     
     
       19. The optical device according to  claim 16 , wherein:
 the measurement step is a first measurement step; 
 the positioning device is configured, at least in a second measurement step, to determine a position of the movable unit, moved by the drive unit according to a predefinable scheme in the at least one degree of freedom; 
 the first measuring device is configured to determine in a third measurement a first variable which is representative of the position of the movable unit in the at least one degree of freedom and to pass it to the control device; 
 the second measuring device is configured to determine in a fourth measurement, using the reference element, a second variable which is representative of the position of the movable unit in the at least one degree of freedom and to pass it to the control device; and 
 the control device is configured, in the calibration step, to calibrate the first measuring device using the results of the first measurement, the second measurement, the third and fourth measurements. 
 
     
     
       20. The device according to  claim 16 , wherein the position measuring device is:
 a) a position measuring device of a mask table of a microlithography device; 
 b) a position measuring device of a substrate table of a microlithography device; 
 c) a position measuring device of a substrate table of a substrate inspection device; or 
 d) a position measuring device of a mask table of a mask inspection device.